Coffee acidity is a divisive term in coffee brewing. For some, it signals sharp, sour flavours. For others, it’s a revered attribute of a high-quality drink.
Lee este artículo en español ¿Cómo Acentuar (o Reducir) la Acidez Cuando Preparas Café?
Make no mistake: sour coffee is unpleasant. But vibrant, bright, and complex acidity, the kind that reminds you of stone fruits or a sweet tangerine, is highly appreciated by coffee professionals and specialty coffee consumers.
Whether your aim when brewing is to highlight a coffee’s natural, juicy acidity or avoid nasty sour notes, the good news is that you can.
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Brewing coffee with the Behmor Connected. Credit: Behmor
Know What You’re Brewing
You can only accentuate the characteristics that are already in your coffee beans. For that reason, it’s important to know what you have on your hands.
Is it a hard- or soft-bean coffee? Hard beans are grown at cooler temperatures (which normally, but not always, correlate with higher elevation). Generally, the harder the bean, the more fruitiness and acidity it is likely to have.
How was it processed: wet/washed, natural/dry, or honey/pulped natural? This is how the coffee beans (which are actually seeds) were removed from the coffee fruit, or cherry. It has a big impact on the flavour of the coffee. Naturals and honeys, if processed well, tend to have enhanced sweetness and body, while washed processing lends itself to a clean coffee profile – the kind of profile that allows complex acidity to shine.
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Then there’s the roast: is it dark, medium or light? The darker the roast, the more you taste the roasting process than the coffee itself. A very dark roast will often be bitter, while lighter roasts will display more of the coffee’s natural acidity.
Natural, honey, washed, and roasted coffee beans. Credit: Ana Valencia for Behmor
Water: The Biggest Ingredient in Your Coffee
Coffee is 94–98% water. This means that its flavour can be affected by the water used during brewing.
Let’s start with hard and soft water. Hard water has a high mineral content in terms of magnesium and calcium. Soft water has a low mineral content.
Steve Cuevas is 2017’s US Cup Tasters Champion, which means he had to identify different coffees and their qualities by taste and smell alone. “At higher concentrations,” he tells me, “some minerals act as ‘acid buffers’ and will lower the perception of acid… It will still be there, but it won’t taste like it. It will also extract the coffee faster, pulling out bitterness if you brew past two minutes,” he explains.
Thomas Chandler is a coffee roaster, molecular biologist, and chemist. He explains that carbonate is an “acid buffer”: the more carbonate in the water, the less acidic the brew. But he adds that this is not the only compound buffer and that carbonate’s ability to do this depends on the presence or absence of other compounds.
Soft water tends to be rich in sodium. Steve says that this allows any acidity to shine. That doesn’t mean it’s always better. Christopher Hendon, a chemist from the University of Bath, and Maxwell Colonna-Dashwood discovered that water with high calcium and magnesium levels will extract more flavours and acids. At Barista Camp 2015, Colonna-Dashwood explained that this water would also benefit from the presence of buffers.
So, what’s the solution? Whether we’re making coffee at home or in a café, this information can improve our brew. If your coffee is sour, dull, and lifeless but you know it isn’t due to the coffee or your brewing, try changing the water. Use filter or bottled water to see how your coffee changes.
Coffee being served. Credit: Behmor
Tweaking Your Coffee Recipes to Control Acidity
Water may be the biggest ingredient in your coffee, but it’s the combination of coffee and water that creates its flavour – meaning that how you combine them will affect the brew’s taste.
Mixing water and coffee leads to extraction: the slow diffusion of coffee flavour and aroma compounds from the beans into the water. And the amount of coffee and water, brew time, coffee grind size, water temperature, and more all affect how many of those compounds are extracted.
This doesn’t just create a “stronger” or “weaker” cup of coffee, because certain flavour and aroma compounds are extracted at different times.
Early in the extraction process, you’ll get the fruity acids. Next comes sweetness and balance, and then, finally, bitterness. This means that under-extracted coffee will taste sour while over-extracted coffee will be bitter. You want the Goldilocks of coffee extraction: sweetness, balance, body, and the perfect amount of acidity for your preferences.
Discover more in Coffee Science: Breaking Down Where Flavour Comes From
Roasted beans and the brew they become. Credit: Behmor
Grind Size & Extraction
There really is no one-size-fits-all grind profile. However, there are some basic rules that will help you brew for greater, or less, acidity.
A coarser grind size will slow down the rate of extraction because there is less surface area. (Note that extraction rate, the speed at which flavours and aromas are extracted, is different to brew time, the amount of time that the ground coffee spends in the water.) This means that a coarser grind should lead to greater sparkling acidity – or, if taken too far, sourness.
Want more acidity? Grind coarser. Less acidity? Grind finer.
Of course, grind size is just one of many factors. The ideal grind size will also vary according to the coffee. For example, darker roasted coffees tend to be more soluble and will, therefore, extract quicker. Often, a coarser grind will suit them better.
Discover more! Read A Guide to Coffee Grind Size, Consistency, & Flavour
Coarse and fine coffee grinds. Credit: Nicholas Yamada
Brew Time, Extraction, & Acidity
Another big factor in coffee extraction is brew or contact time. The longer the brew time, the more is being extracted.
You can use beans you like, good-quality water, and the ideal grind size, and still end up with coffee that’s too sour or too dull if you have the wrong brew time.
As the team at Barista Hustle emphasise, grind size doesn’t change what is being extracted. It just changes when it’s being extracted. So if you have a coarse grind size but a long brew time, you still won’t get much acidity in your cup. And if you have a fine grind size but a very short extraction time, the cup might still taste sour.
So, shorten or lengthen your brew time to taste more or less acidity, respectively.
Fruity coffee with a fruity scone. Credit: Ana Valencia for Behmor
Using Water Temperature to Highlight Acidity
Your extraction rate can also be impacted by your water temperature. Joe Behm is the Founder and CEO of Behmor, and he designs and manufactures SCA-certified smart coffee brewers and roasters. The Behmor Brewer offers 1°F temperature control so users can control exactly how much acidity, sweetness, and more is in their coffee.
The hotter the water, the quicker the compounds extract. The cooler the temperature, the slower the extraction. However, some compounds won’t extract at certain temperatures (this is why cold brew has sweet, smooth taste and limited acidity). It will also interact with your grind size, brew time, and more.
Joe favours a higher temperature and shorter brew time. “To bring out a brew’s acidity, I stick to the 204ºF/95ºC to 205ºF/96ºC range,” he tells me.
Steve agrees – providing the water quality is good. He says that some people use lower temperatures to avoid bitterness. With good water (and controlling all other variables), he gets a more pronounced acidity at 94ºC/202ºF than 91ºC/197ºF.
Coffee being brewed in a Behmor Brazen Plus. Credit: Behmor
The wonderful thing about brewing our own coffee is that we get to drink it exactly the way we like it. And although it gets a little technical at times, mastering these concepts will enable us to brew a delicious cup of coffee every single time.
So, go ahead and tweak your coffee recipes. Try different types of water. And experiment with water temperature. Because even just a 1ºF difference may be the key to turning a dull or sour brew into a coffee full of bright, fruity acidity.
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